Immunohistochemical localization of exocrine enzymes in normal rat pancreas

On the basis of morphological and biochemical differences, the exocrine pancreatic tissue has been divided in peri- and teleinsular regions. In the present study the enzymatic profile of these regions has been investigated by the immunofluorescent technique using antibodies against nine pancreatic enzymes (alpha-amylase, lipase, chymotrypsinogen A, trypsinogen, elastase, carboxypeptidase A and B, DNase and RNase A). These antibodies were specific to their antigens without cross reaction. By immunofluorescence, most acinar cells of the normal rat pancreas were positive to the nine enzymes tested. However, an inhomogeneity in the staining pattern was found; specifically, the cells located in the periinsular region of many islets showed a brighter fluorescence than acinar cells in the teleinsular tissue. These data add a new parameter to describe the inhomogeneity of the exocrine pancreas.

Ultrastructural localization of intracellular antigens by the use of protein A-gold complex

An immunocytochemical technique for the demonstration of intracellular antigens (secretory proteins) on thin sections is reported. Staphylococcal protein A which reacts with the Fc fragment of IgG molecules was labeled with colloidal gold as a marker. The antigenic sites were visualized on aldehyde-fixed and Epon-embedded tissue in a two step procedure. The specific antisera were applied to thin sections for binding to the antigens and then visualized by the protein A-gold complex. By using this technique different secretory proteins of the exocrine and endocrine pancreas were localized. The protein A-gold technique is proposed as a general method for visualization of antigenic sites on thin sections.

[Metabolism of capillary endothelium tissue and its abnormalities in diabetes mellitus (author's transl)]

Glucose is the major energetic substrate of blood capillary endothelium; aerobic glycolysis is quantitatively the most important pathway. Insulin has no direct effect on glucose utilization. The glucokinase activity of the capillary endothelium is undetectable and the plasma cell membrane is freely permeable to glucose. All pathways of glucose utilization are stimulated by a high ambient glucose concentration: intracellular sorbitol accumulation and glucose-carbon incorporation into basement membrane collagen are most sensitive to the glucose effect. During chronic hyperglycemia, the amino acid composition of the basement membrane is modified and its capacity to incorporate glucose is enhanced. The glucose induced alterations of the blood capillary metabolism may contribute to the development of the diabetic microangiopathy.

Diffusion permeability of an isolated rete mirabile

The rete mirabile of the swimbladder of the eeel is a countercurrent exchange organ composed of alternately disposed and venous capillaries. A countercurrent perfusion of these was set up by isolating arterial input and outflow, and venous input and outflow, and perfusing each set of capillaries with oxygenated albumin-containing Krebs-Ringer bicarbonate buffer. Constant arterial infusions containing tracer albumin, inulin, 3-O-methylglucose, urea, and water were begun and tracer concentrations at the outlets of arterial and venous beds were determined. Capillary permeabilities were determined from the resulting steady state values. The method of calculation of permeability values from the data acquired in the rete involves no approximations and appears to yield unequivocal values. For the solutes, the values appear compatible with transcapillary passage by free diffusion. No evidence of increasing restriction (in comparison to the diffuse coefficients) was found over the range of molecular sizes explored. The permeability for labeled water, in relation to the solutes, was too high, and this augmentation was attributed to the larger surface available for its exchange. Despite this larger value, labeled water did not undergo flow-limited exchange. A significant barrier to its distribution is present in this capillary system.

Studies of the capillary basal lamina. I. Ultrastructure of the red body of the eel swimbladder

The rete mirabile of the eel swimbladder is a vascular organ in which arterial andvenous capillaries alternate in regular fashion. The endothelium of the arterial capillaries is high, whereas that of the venous capillaries is thin and fenestrated. Endothelial cells and pericytes are the only cells found in the rete. A tubular systemin the arterial endothelial cells is connected with the organelles. The basal laminaeof both capillaries are similiar to those of mammalian capillaries of the same type. They present three layers of different electron density and have a high fibrillar pattern.A fine fibrillar material and dense fibrils appear in the cisternae of the rough endoplasmic reticulum and in large vacuoles of endothelial cells and pericytes: these cells areapparently involved in the synthesis of their lamina. Since the rete mirable ofthe eel swimbladder is a pure vascular preparation, it is most useful for the study of themorphology, the permeability, and the metabolism of the endothelial cells and for the analysis of the chemical structure of their basil laminae.

Studies of the capillary basal lamina. II. Preparation, chemical composition, andmetobolic properties

Large amounts of basal laminae material can be extracted by sonic disruption from the capillary tissue of the rete mirabile of the eel swimbladder. The extracted basil laminae material has the same fibrillar pattern as that found in the intact tissue. Thechemical composition is similiar to that of other basil laminae isolated from tissues inmammals, with high content of glycine, proline, hydroxyproline, lysine, and hydroxylysine. The mono- and disaccharide units linked to the hydroxylysine are also present. Of all the pathways of glucose utilization, the 'C-glucose incorporation into the basallamina glycoproteins is the most sensitive to the medium glucose concentration. The glucosyltransferase activity seems stimulated to a plateau value of saturation when the medium glucose concentration is raised from 5 to 20 mm. The 'C-labeled amino acid incorporation into the basal laminae glycoproteins is not affected bythe medium glucose concentration. The results obtained in this study allow for a hypothesis which links the biochemical, morphologic, and functional properties of various typesof basal laminae in normal and hyperglycemic conditions.

The capillary endothelium in the rete mirabile of the swimbladder of the eel (Anguilla anguilla): functional and ultrastructural aspects

The rete mirabile of the swimbladder of the eel is a network of straight capillaries, one against the other, in which an arterial capillary alternates with a venous capillary. The function of these capillaries is to allow the swimbladder to concentrate oxygen by a hairpin countercurrent multiplication mechanism.Electron microscopy shows a very large number of channels in the endothelial cells and most of the channels have alternating dilatations and constrictions as though fixed in a condition of peristalsis. The findings suggest that there is a continuity between the organelles and indicate that the hairpin countercurrent multiplication mechanism may be dependent upon a continuous active return system composed of the membrane-bound channels.